In manufacturing electronic devices, dopants or impurities are introduced into a substrate to alter the substrate's mechanical, optical, or electrical property. In manufacturing memory devices, boron ions are introduced into a silicon substrate. As boron ions and silicon atoms in the crystal lattice have different electrical property, introduction of sufficient boron ions may alter the electrical property of the substrate. Among others, ion implantation technique may be used to introduce the dopants. Referring to FIG. 1, there is shown a block diagram of a typical ion implantation system 100 to perform the ion implantation. The ion implantation system 100 may comprise an ion source 102, beam-line components 104; and an end station 106. In the end station, a substrate 112 and a platen 114 supporting the substrate 112 are disposed.
In the ion source 102, feed material having desired species, such as boron, are introduced and ionized to form ions 10 of desired species. The ions 10 are then extracted from the ion source 102 and directed toward the beam-line components 104. Much like a series of optical lenses that manipulate a light beam, the beam-line components 104 can filter, focus, and manipulate the ions into an ion beam 10 having prescribed energy, and direct the ion beam 10 toward the end station 106. In the end station 106, the substrate 112 supported by the platen 114 is exposed to the ion beam 10. Typically, the substrate 112 and the platen 114 can be moved in one or more dimensions (e.g., translate, rotate, and tilt) by an apparatus, sometimes referred to as a “roplat.”
A solar cell, another silicon substrate based device, may also be manufactured by introducing property altering dopants into the silicon substrate. In the past, the dopants have been introduced via diffusion process where dopant containing glass or paste is disposed on the silicon substrate. Thereafter, the substrate is heated, and the dopants are diffused into the substrate.
Although the diffusion process may be cost effective, the process has many drawbacks. In manufacturing solar cells, selective doping is performed where only certain regions of the substrate are implanted with dopants. However, selective doping process using the diffusion process may be difficult to achieve as the process is difficult to control. The process may result in imprecise doping or formation of non-uniform doping regions. In addition, voids or air bubbles, or other contaminants may be introduced into the substrate along with the dopants during the diffusion process.
To address such drawbacks, doping via ion implantation process has been proposed. In the proposed process, the substrate is coated with photoresist layer, and lithographic process is performed to pattern and expose portions of the substrate. Thereafter, the ion implantation is performed, and dopants are implanted into the exposed portions. The process, although achieves precise selective doping, is not inexpensive. Additional steps and time to coat, pattern, and remove the photoresist, each of which adds costs to the manufacturing process, are required. Any added cost in manufacturing the solar cell would decrease the solar cell's ability to generate low cost energy. Meanwhile, any reduced cost in manufacturing high-performance solar cells with high efficiency would have a positive impact on the implementation of solar cells worldwide. This will enable the wider availability and adoption of clean energy technology.
Accordingly, a new technique is needed.